There is a known homologous analysis method based on a DNA base sequence as a method for identifying the type of a cell, and the method is widely used, for example, for classification and identification of a microorganism (see Patent Literature 1, for example). The method includes the steps of extracting a DNA from a test cell and determining a DNA base sequence in an area that is highly preserved in every organism, such as a rRNA gene. The method further includes the steps of searching a database containing a large number of data on DNA base sequences of known cells for the determined DNA base sequence, and picking up a base sequence showing high similarity to the DNA base sequence in the test cell. The method finally includes the step of determining that an organism species from which the selected base sequence is derived is the same species as the test cell or a species related to the test cell.
The method of this type using a DNA base sequence, however, requires relatively long time to extract a DNA from a test cell and to determine a DNA base sequence, and therefore has a difficulty in performing a quick cell identification.
In view of the fact described above, a method of identifying a cell based on a mass spectrum pattern obtained by performing mass spectrometry on a test cell has been increasingly used in recent years (see Patent Literature 2, for example). The method includes a step of first analyzing a solution containing proteins extracted from a test cell or a suspension liquid containing the test cell with a mass spectrometer using MALDI-MS (matrix assisted laser desorption/ionization-mass spectrometry) or any other mild ionizing method. The method further includes a step of comparing the resultant mass spectrum pattern with mass spectrum patterns of known cells contained in a database to identify the test cell. Mass spectrometry not only quickly provides an analysis result from a trace amount of cell specimen but also readily allows successive analysis of a large number of specimens. The cell identification method of this type using mass spectrometry therefore allows cell identification to be readily and quickly performed.